The invention relates to a device for superimposing rotational speeds, with an input shaft (1) and an output shaft (2) disposed in the longitudinal direction with respect to one another, a carrier system (11a, 11b) disposed stationarily on the vehicle body, in which the input shaft (1) and the output shaft (2) are positioned rotatably such that they are at least partially bearing supported and with an auxiliary drive (6, 7) with a stator (7) disposed on the carrier system (11a, 11b) and with a rotor rotatably bearing-supported axially parallel with the input shaft (1).
The invention relates in particular to a rotational speed superposition device with auxiliary drive for a steering system for free-riding or non-trackbound motor vehicles which superimposes the rotational speeds of the auxiliary drive and of the steering interventions on the steering wheel by the driver and transfers them to the steering movements of the wheels.
Such rotational speed superposition devices are also referred to in prior art, to the extent they are applied for steering systems, as rotational angle superimposing devices. Rotational speed superposition or rotational angle superposition are synonyms.
Within prior art a number of such systems is known, wherein the rotational superposition gearing is realized by a planetary gearing or also by a worm wheel gearing.
DE 19 823 721 A1 introduces such a rotational speed superposition device. Through a steering wheel a housing is here driven in which toothings of an internal gear wheel of two planetary gearings are located. An electric motor disposed in the housing drives the sun wheel of the first planetary gearing. The planet carrier of the first planetary gearing drives the sun wheel of the second planetary gearing. The planets of the second planetary gearing are supported on the internal gear wheel of the housing and the planet carrier is connected with the output shaft. In the depicted embodiment the driving of the sun wheel of the first planetary gearing is realized directly through the rotor of the electric motor. Through an appropriate actuation of the electric motor, the desired rotational speed superpositions can be produced. However, this solution shown in prior art entails some decisive disadvantages. Such gearings are comprised of a large number of structural parts. Two internal crown gear wheels or planetary gearings are necessary. The production of the parts is highly complex and expensive. The large number of tooth engagements leads to very high requirements made of the precision in order to avoid play. The entire device, including the motor housing, must further be rotated by the driver when steering. Moreover, a further disadvantage lies in the complex coupling-in of the electric energy for the electric motor.
In further prior art, DE 19 852 447 A1, a solution is introduced for the superposition of rotational speed in which an electric motor is coupled via a worm drive gearing, implemented as a planetary gearing, to the superposition gearing. The gearing unit is here disposed stationarily on the vehicle body. However, this solution also entails a number of disadvantages. The coupling via a worm gearing leads to very low efficiency of the rotational speed transmission. The arrangement furthermore requires considerable installation space, which is not very flexible due to the geometrically determined positions of the components relative to one another. The production of the parts is here also complex and expensive and the requirements made of the production tolerances correspondingly high.